Telecommunications systems, cable television systems and data communication networks use optical networks to rapidly convey large amounts of information between remote points. In an optical network, information is conveyed in the form of optical signals through optical fibers. Optical fibers comprise thin strands of glass capable of transmitting the signals over long distances with very low loss.
Optical networks often employ wavelength division multiplexing (WDM), including dense wavelength division multiplexing (DWDM), to increase transmission capacity. In WDM networks, a number of optical channels are carried in each fiber at disparate wavelengths. Network capacity is based on the number of wavelengths, or channels, in each fiber and the bandwidth, or size of the channels.
WDM networks use optical cross connects (OXC) or reconfigurable or other optical add/drop multiplexing (OADM) nodes to add, drop, and switch traffic in the network. OXCs and other network elements typically include ingress line amplifiers to compensate for line losses and egress line amplifiers to compensate for node losses. Within the node, variable attenuators (VATs) are used on demultiplexed signals to limit wavelength loss variation. VATs may be integrated with an optical cross connect (OXC) and an array wave-guide grating (AWG) of a node.